OPERATION MANAGEMENT NOTES

the centers in such a way that processing and setups are minimized along with idle time and throughput time. Two approaches are used for loading work centers: infinite loading and finite loading. With infinite loading jobs are assigned to work centers without regard for capacity of the work center. Priority rules are appropriate for use under the infinite loading approach. Jobs are loaded at work centers according to the chosen priority rule. This is known as vertical loading. Finite loading projects the actual start and stop times of each job at each work center. Finite loading considers the capacity of each work center and compares the processing time so that process time does not exceed capacity. With finite loading the scheduler loads the job that has the highest priority on all work centers it will require. Then the job with the next highest priority is loaded on all required work centers, and so on. This process is referred to as horizontal loading. The scheduler using finite loading can then project the number of hours each work center will operate. A drawback of horizontal loading is that jobs may be kept waiting at a work center, even though the work center is idle. This happens when a higher priority job is expected to arrive shortly. The work center is kept idle so that it will be ready to process the higher priority job as soon as it arrives. With vertical loading the work center would be fully loaded. Of course, this would mean that a higher priority job would then have to wait to be processed since the work center was already busy. The scheduler will have to weigh the relative costs of keeping higher priority jobs waiting, the cost of idle work centers, the number of jobs and work centers, and the potential for disruptions, new jobs and cancellations. If the firm has limited capacity (e.g., already running three shifts), finite loading would be appropriate since it reflects an upper limit on capacity. If infinite loading is used, capacity may have to be increased through overtime, subcontracting, or expansion, or work may have to be shifted to other periods or machines. SEQUENCING Sequencing is concerned with determining the order in which jobs are processed. Not only must the order be determined for processing jobs at work centers but also for work processed at individual work stations. When work centers are heavily loaded and lengthy jobs are involved, the situation can become complicated. The order of processing can be crucial when it comes to the cost of waiting to be processed and the cost of idle time at work centers. There are a number of priority rules or heuristics that can be used to select the order of jobs waiting for processing. Some well known ones are presented in a list adapted from Vollmann, Berry, Whybark, and Jacobs (2005): • Random (R). Pick any job in the queue with equal probability. This rule is often used as a benchmark for other rules. • First come/first served (FC/FS). This rule is sometimes deemed to be fair since jobs are processed in the order in which they arrive. • Shortest processing time (SPT). The job with the shortest processing time requirement goes first. This rule tends to reduce work-in-process inventory, average throughputtime, and average job lateness. • Earliest due date (EDD). The job with the earliest due date goes first. This seems to work well if the firm performance is judged by job lateness. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 51

• Critical ratio (CR). To use this rule one must calculate a priority index using the formula (due date–now)/(lead time remaining). This rule is widely used in practice. • Least work remaining (LWR). An extension of SPT, this rule dictates that work be scheduled according to the processing time remaining before the job is considered to be complete. The less work remaining in a job, the earlier it is in the production schedule. • Fewest operations remaining (FOR). This rule is another variant of SPT; it sequences jobs based on the number of successive operations remaining until the job is considered complete. The fewer operations that remain, the earlier the job is scheduled. • Slack time (ST). This rule is a variant of EDD; it utilizes a variable known as slack. Slack is computed by subtracting the sum of setup and processing times from the time remaining until the job's due date. Jobs are run in order of the smallest amount of slack. • Slack time per operation (ST/O). This is a variant of ST. The slack time is divided by the number of operations remaining until the job is complete with the smallest values being scheduled first. • Next queue (NQ). NQ is based on machine utilization. The idea is to consider queues (waiting lines) at each of the succeeding work centers at which the jobs will go. One then selects the job for processing that is going to the smallest queue, measured either in hours or jobs. • Least setup (LSU). This rule maximizes utilization. The process calls for scheduling first the job that minimizes changeover time on a given machine. These rules assume that setup time and setup cost are independent of the processing sequence. However, this is not always the case. Jobs that require similar setups can reduce setup times if sequenced back to back. In addition to this assumption, the priority rules also assume that setup time and processing times are deterministic and not variable, there will be no interruptions in processing, the set of jobs is known, no new jobs arrive after processing begins, and no jobs are canceled. While little of this is true in practice, it does make the scheduling problem manageable. GANTT CHARTS Gantt charts are named for Henry Gantt, a management pioneer of the early 1900s. He proposed the use of a visual aid for loading and scheduling. Appropriately, this visual aid is known as a Gantt chart. This Gantt chart is used to organize and clarify actual or intended use of resources within a time framework. Generally, time is represented horizontally with scheduled resources listed vertically. Managers are able to use the Gantt chart to make trial-and- error schedules to get some sense of the impact of different arrangements. There are a number of different types of Gantt charts, but the most common ones, and the ones most appropriate to our discussion, are the load chart and schedule chart. A load chart displays the loading and idle times for machines or departments; this shows when certain jobs are scheduled to start and finish and where idle time can be expected. This can help the scheduler redo loading assignments for better utilization of the work centers. A schedule chart is used to monitor job progress. On this type of Gantt chart, the vertical axis shows the orders or jobs in progress while the horizontal axis represents time. A quick glance at the chart reveals which jobs are on schedule and which jobs are on time. Gantt charts are the most widely used scheduling tools. However, they do have some limitations. The chart must be DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 52

repeatedly updated to keep it current. Also, the chart does not directly reveal DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 53

costs of alternate loadings nor does it consider that processing times may vary among work centers. SCHEDULING SERVICE OPERATIONS The scheduling of services often encounters problems not seen in manufacturing. Much of this is due to the nature of service, i.e., the intangibility of services and the inability to inventory or store services and the fact that demand for services is usually random. Random demand makes the scheduling of labor extremely difficult as seen in restaurants, movie theaters, and amusement parks. Since customers don't like to wait, labor must be scheduled so that customer wait is minimized. This sometimes requires the use of queuing theory or waiting line theory. Queuing theory uses estimate arrival rates and service rates to calculate an optimum staffing plan. In addition, flexibility can often be built into the service operation through the use of casual labor, on-call employees, and cross-training. Scheduling of services can also be complicated when it is necessary to coordinate and schedule more than one resource. For example, when hospitals schedule surgery, not only is the scheduling of surgeons involved but also the scheduling of operating room facilities, support staff, and special equipment. Along with the scheduling of classes, universities must also schedule faculty, classrooms, labs, audiovisual and computer equipment, and students. To further complicate matters, cancellations are also common and can add further disruption and confusion to the scheduling process. Instead of scheduling labor, service firms frequently try to facilitate their service operations by scheduling demand. This is done through the use of appointment systems and reservations. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 54

MAINTENANCE MANAGEMENT Maintenance management is the process of overseeing maintenance resources so that the organization does not experience downtime from broken equipment or waste money on inefficient maintenance procedures. Maintenance management software programs can assist with the process. The primary objectives of maintenance management are to schedule work efficiently, control costs and ensure regulatory compliance. Importance Maintenance management is essential to the success of any organization because a poorly- organized maintenance program can bring the entire company to a halt. For instance, if maintenance employees are fixing a broken photocopier instead of an essential piece of production equipment, a factory can stop producing anything. If the maintenance manager doesn't understand company processes well enough to know what is most important, this type of scheduling problem becomes more likely. If the maintenance manager schedules four employees when only one is needed, the company will lose money. If materials such as chemicals are not stored and disposed of properly, the company could have compliance issues. IMPORTANCE AND OBJECTIVES OF MAINTENANCE MANAGEMENT Maintenance is an important factor in quality assurance, which is another basis for the successful competitive edge. Inconsistencies in equipments lead to variability in product characteristics and result in defective parts that fail to meet the established specifications. Beyond just preventing break downs, it is necessary to keep equipments operating within specifications (i.e. process capability) that will produce high level of quality. Good maintenance management is important for the company’s cost control. As companies go in for automation to become more competitive, they increasingly rely on equipments to produce a greater percentage of their output. It becomes more important that, equipments operate reliably within specifications. The cost of idle time is higher as equipment becomes more high- tech and expensive e.g. NC/CNC machines and robots. Dependability of service is one of the performance measures by which a company can distinguish itself from others. To establish a competitive edge and to provide good customer service, companies must have reliable equipments that will respond to customer demands when needed. Equipments must be kept in reliable condition without costly work stoppage and down time due to repairs, if the company is to remain productive and competitive. Many manufacturing organizations, particularly those with JIT (Just-In-Time) programs are operating with inventories so low that, they offer no protection in the event of a lengthy equipment failure. Beyond the cost of idle equipment, idle labor, and lost ales that can result from a breakdown, there is a danger of permanently losing market shares to companies that are more reliable. Maintenance function can help prevent such as occurrence. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 55

Organizations like airlines and oil refineries have huge investments in the equipment. Equipment failure will be disastrous for such companies. They need proper maintenance to keep the equipment in good condition. Impact of Poor Maintenance Maintenance operations include all efforts to keep production facilities and equipments in an acceptable operating condition. Failure or ml-functioning of machines and equipments in manufacturing and service industries have a direct impact on the following: 1. Production capacity: Machines idled by breakdowns cannot produce, thus the capacity of the system is reduced. 2. Production costs: Labor costs per unit rise because of idle labor due to machine breakdowns. When machine malfunctions result in scrap, unit labor and material costs increase. Besides, cost of maintenance which includes such costs as costs of providing repair facilities, repair crews, preventive maintenance inspections, spare parts and stand by machines will increase as machines break down frequently. 3. Product and service quality: Poorly maintained equipments produce low quality products. Equipments that have not been properly maintained have frequent break downs and cannot provide adequate service to customers. For example, air craft fleets of the airline, railway and road transport services not maintained well can result in poor service to customers. 4. Employee or customer safety: Worn-out equipment is likely to fail at any moment and these failures can cause injuries to the workers, working on those equipments. Products such as two wheelers and automobiles, if not serviced periodically, can break down suddenly and cause injuries to the stress. 5. Customer satisfaction: When production equipments break own, products often can not be produced according to the master production schedules, due to work stoppages. This will lead to delayed deliveries of products to the customers. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 56

Objectives of Maintenance Management • The following are some of the objectives of maintenance management: • Minimizing the loss of productive time because of equipment failure (i.e. minimizing idle time of equipment due to break down). • Minimizing the repair time and repair cost. • Minimizing the loss due to production stoppages. • Efficient use of maintenance personnel and equipments. • Prolonging the life of capital assets by minimizing the rate of wear and tear. • To keep all productive assets in good working conditions. • To maximize efficiency and economy in production through optimum use of facilities. • To minimize accidents through regular inspection and repair of safety devices. • To minimize the total maintenance cost which includes the cost of repair, cost of preventive maintenance and inventory carrying costs, due to spare parts inventory. • To improve the quality of products and to improve productivity. Types of Maintenance 1. Breakdown maintenance It means that people waits until equipment fails and repair it. Such a thing could be used when the equipment failure does not significantly affect the operation or production or generate any significant loss other than repair cost. 2. Preventive maintenance ( 1951 ) It is a daily maintenance ( cleaning, inspection, oiling and re-tightening ), design to retain the healthy condition of equipment and prevent failure through the prevention of deterioration, periodic inspection or equipment condition diagnosis, to measure deterioration. It is further divided into periodic maintenance and predictive maintenance. Just like human life is extended by preventive medicine, the equipment service life can be prolonged by doing preventive maintenance. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 57

2a. Periodic maintenance ( Time based maintenance - TBM) DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 58

Time based maintenance consists of periodically inspecting, servicing and cleaning equipment and replacing parts to prevent sudden failure and process problems. 2b. Predictive maintenance This is a method in which the service life of important part is predicted based on inspection or diagnosis, in order to use the parts to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. It manages trend values, by measuring and analyzing data about deterioration and employs a surveillance system, designed to monitor conditions through an on-line system. 3. Corrective maintenance ( 1957 ) It improves equipment and its components so that preventive maintenance can be carried out reliably. Equipment with design weakness must be redesigned to improve reliability or improving maintainability 4. Maintenance prevention ( 1960 ) It indicates the design of a new equipment. Weakness of current machines are sufficiently studied ( on site information leading to failure prevention, easier maintenance and prevents of defects, safety and ease of manufacturing ) and are incorporated before commissioning a new equipment. Breakdown maintenance is maintenance performed on equipment that has broken down and is unusable. It is based on a breakdown maintenance trigger. It may be either planned or it can be unplanned. An example of planned maintenance is run-to- failure maintenance, while examples of unplanned maintenance include corrective maintenance and reactive maintenance. Breakdown maintenance can be more costly than preventative maintenance. Maintenance Policies: 1. Breakdown (repair) maintenance 2. Preventive maintenance Breakdown maintenance is emergency based policy in which the plant or equipment is operated until it fails and then it is brought back into running condition by repair. The maintenance staffs locate any mechanical, electrical and any other fault to correct it immediately. Preventive maintenance policy prevents the probable breakdown and it ensures smooth and uninterrupted production by anticipating the breakdowns (failures) and taking corrective actions: The preventive maintenance policy has four forms: (a) Time based: Page 59 DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

Which means doing maintenance at regular intervals? It is time dependent rather than usage dependent. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 60

(b) Work based: Maintenance after a set of operating hours of volume of work produced. (c) Opportunity based: Where repair and replacement takes place when the equipment or system is available. (d) Condition based: Which often relies on planned inspection to reveal when maintenance is required? Preventive maintenance is used to delays or prevents the breakdown of equipment and also to reduce the seventy of any breakdowns that occur. Two aspects of preventive maintenance are: 1. Inspection: Inspection of critical parts will indicate the need for replacement or repair well in advance of probable breakdown. Regular inspection conducted by either by equipment or operator or by maintenance department is the most important direct means of increasing equipment reliability. 2. Servicing: Routine cleaning, lubrication and adjustment may significantly reduce wear and hence prevent breakdowns. Frequently such duties are carried out by equipment operator or may be carried out by maintenance department. Preventive versus Breakdown Maintenance: Preventive maintenance is the routine inspection and service activities designed to detect potential failure conditions and make minor adjustments or repairs that will help prevent major operating problems. Breakdown maintenance is the emergency repair and it involves higher cost of facilities and equipment that have been used until they fail to operate. Effective preventive maintenance programmes for equipment requires properly trained personnel, regular inspection DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 61

and service and has to maintain regular records. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 62

Preventive maintenance is planned in such a way that it will not disturb the normal operations hence no down time cost of equipment. Breakdown maintenance stops the normal activities and the machines and the operators are rendered idle till the equipment is brought back to normal condition of working DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 63

UNIT –III QUALITY CONTROL Meaning and Importance: Present era is the ‘Era of Quality’.In this age of cutthroat competition and large scale production, only that manufacturer can survive who supplies better quality goods and renders service to-the consumers. In fact quality control has become major consideration before establishing an industrial undertaking. Proper quality control ensures most effective utilisation of available resources and reduction in cost of production. The word quality control comprises of two words viz., quality and control. It would be appropriate to explain these two words separately to understand clearly the meaning of quality control. According to Dr. W.K. Spriegel “The quality of a product may be defined as the sum of a number of related characteristics such as shape, dimension, composition, strength, workmanship, adjustment, finish and colour”. In the words of John D. McIIellan, “Quality is the degree to which a product conforms to specifications and workmanship standards”. It is clear from these definitions that quality refers to various characteristics of a product and their excellence. Quality is a relative term and is never absolute depending upon the use of the product and circumstances under which it is used. To achieve and maintain a satisfactory level of quality of products is a very difficult task. It involves many steps to be undertaken viz: (a) Product must possess a minimum level of quality so that it could be easily sold in the market. (b) In order to measure quality, accurate standard measurements must be established. (c) Reasonable deviation from the pre-determined standards must be determined. (d) Satisfactory level of quality must be achieved with a minimum cost. Control refers to the use of all the ways and means whereby quality standards could be maintained. Control precisely aims at bringing the product up to predetermined standards by minimising deviations from established and present standards. According to Henry Fayol, “Control consists in verifying whether everything occurs in conformity with the plan Page 64 adopted, the instructions issued and principles established. It has objected to point out weaknesses and errors in order to rectify them and prevent recurrence. It operates on everything things, people, actions”. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

In the absence of effective control over production operations, desired quality in products to be produced cannot be DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 65

achieved. How it may be pointed out here that words quality and control cannot be studied separately in this context but as ‘Quality Control’. Quality control is concerned with the control of quality of the product during the process of production. It aims at achieving the predetermined level of quality in a product. In other words quality control is concerned with controlling those negative variances which ultimately affect the excellence of a manufacturer in producing the products. —J.A. Shubin. “Quality control is used to connote all those activities which are directed for defining, controlling and maintaining quality”. Objectives of quality control: Following are the important objectives of quality control: 1. To establish the desired quality standards which are acceptable to the customers? 2. To discover flaws or variations in the raw materials and the manufacturing processes in order to ensure smooth and uninterrupted production. 3. To evaluate the methods and processes of production and suggest further improvements in their functioning. 4. To study and determine the extent of quality deviation in a product during the manufacturing process. 5. To analyse in detail the causes responsible for such deviation. 6. To undertake such steps which are helpful in achieving the desired quality of the product. ISO Quality Control Standards and Specifications Many inspection firms, like AQF, conduct inspections following the ISO Quality Control 9001 Standard. However, sometimes we get requests from a client to use other ISO specifications, like ISO 16949 for the automobile industry. But what is the exact difference between Standards and Specifications? ISO standards are developed according to strict rules to ensure that they are transparent and fair. This requires a lot of negotiation before all 162 national members can reach a consensus that represents the state of the art; In fact, an international Standard requires 75% member approval. To ensure that ISO standards stay up to date, they are reviewed every five years. Technical experts can then decide whether a certain standard is still valid. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 66

However, this obviously takes significant time, while some industries are so fast-moving that the experts are already thinking about the next version when one is being published. Technology changes quickly, and some specifications DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 67

are needed faster than others. Therefore, to meet such needs, ISO has developed different categories of specifications, allowing ratification at an intermediate stage of development before full consensus: Technical Specifications can pass with only 67% approval. There are 715 different ISO Technical Specifications. These Specifications can conflict, as long as they do not conflict with the Standards. Eventually, the aim of Technical Specifications is still to become Standards, but as they are reviewed regularly (no later than 3 years after their publication), they are quite unstable. While newer Specifications may indeed be a bit more au courant, there is no guarantee that it will still be standing come year’s end. Thus, this is why AQF and many other firms generally inspect on the basis of the ISO 9001 Standard. AQF also uses its years of experience in QC to constantly improve our audits. We update our audit template every month to keep up to date on the newest important issues. That being said, ISO 9001 is the base for every audit and is a critical standard to be followed! Concept of Quality Circles (QC): The concept of quality control originated in the U.S. and was taken to Japan by W. Edwards Deming who marked the beginning of revolution in quality control. As quality control awareness increased in Japan, the Japanese companies used statistical quality control to motivate their workers to produce high-quality products. One of the mechanisms used by these companies to improve the quality not only of their products but also the personnel was quality circles which is in practice even today. Quality circle is a group of labour and management who belong to a single department, do same or similar work, meet periodically to discuss and analyse manufacturing problems (for about an hour per week in paid time) and find solutions to quality problems. Rather than developing technical staff that works with management and workers, quality circles train the workers who identify and solve the problems they face during the production process. Quality circle is “an approach to improving quality and reducing the cost of producing a product or service by the voluntary efforts of small groups of workers, who are generally led by a first- line supervisor”. However, the supervisor does not issue orders. The circle members analyze their problems, gather relevant information, find solutions and implement them. The QC members do not receive monetary rewards for presenting solutions to management but receive recognition for their services to the organization. QCs improve the quality of products and the work atmosphere as members feel they are an important part of the organization who can positively contribute to product quality. Though initially started in the manufacturing area, the concept of QCs widely applies in service sector also (banking, insurance etc.). Quality circles are regular short meetings that help to solve work-related problems. Page 68 (a) 5-10 people attend the meeting in work-time. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

(b) Supervisor is nominated and he runs the meeting. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 69

(c) Flip charts, audio-visual equipment, notice boards etc. are utilized. (d) Problem areas are put forward by the group. (e) Problems are prioritized. (f) Information is collected, ideas are generated via brainstorming and force-field analysis. (g) Effectiveness, costs, savings, consequences to other departments etc. are considered. (h) Final solution is put forward to manager and implemented by the quality circle group. Objectives of Quality Circles: Following are the objectives of Quality Circles: • To improve the quality of products. • To improve productivity of the firm. • T o develop sense of confidence in the workers that they can solve their own problems. • To improve employees’ morale. • To improve employees’ job satisfaction. • To develop the personality of employees by making them aware of their importance in the work related areas and work atmosphere. • To improve interpersonal relationship between management and workers. • To improve employees’ motivation and communication within the organisation. Merits of Quality Circles: Quality circles have the following merits: (a) They focus on product quality in a planned way. (b) They train employees to identify their problems, find solutions and implement them without seeking the advise of technical experts. (c) They satisfy members’ higher-order needs of recognition and self-actualisation. (d) They improve members’ participation in work-related problems and enhance their job satisfaction. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 70

(e) They promote productivity, efficiency, cost reduction, design, testing, safety etc. ofthe products. (f) Since teaching is done in an informal way, employees are not burdened with analysing and solving their problems. Rather, they feel motivated to offer suggestions to management. Factors to Make Quality Circles Effective: Quality circles are effective in achieving the goals if they are framed with the following factors in mind: (a) They start with the analysis of small problems and gradually move to bigger problems. (b) Members of the QCs are voluntary and not mandatory to get their maximum support. (c) Members of the QC are taught the basic techniques of problem-solving in an informal way. (d) Before members’ proposal to solve the problem is put to implementation, it is checked by the supervisors. (e) Management supports QC activities rather than leave them totally to the employees. (f) Members are recognised for their contribution to organisational problems. Though quality circles aim at improving organisational climate through constructive workforce, it may not always be able to do so because of the following limitations: 1. Different attitude of managers and workers to perceive the same problem. a. Higher level managers may find it as dilution to their authority for decision-making. b. Workers perceive quality circles as contributors to organisational growth and profits andnot providing personal benefits to them in the form of sharing higher profits. Workers and managers should view QCs as a positive contributor to organisation growth whose benefits would be shared by both managers and workers and not by management only. 2. Workers may not have requisite knowledge, skills and qualities to analyse and solve the organisational problems. They may prefer the directions to come from higher levels than to be self-directed. The very purpose of QC’s is to enhance the decision-making abilities of workers and therefore, workers should be DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 71

trained to make decisions on their own rather than depending on their superiors. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 72

3. Though workers give suggestions in QC, they may not be acceptable and implemented by the management. This can affect the efficiency of QCs. In case the suggestions are not worthy of implementation, managers should convince the members in this regard. Workers should take the arguments positively rather than feeling offended for the same. QUALITY ASSURANCE A definition of quality assurance is: The processes that ensure production quality meets the requirements of customers This is an approach that aims to achieve quality by organising every process to get the product 'right first time' and prevent mistakes ever happening. This is also known as a 'zero defect' approach. In quality assurance, there is more emphasis on 'self-checking', rather than checking by inspectors. Advantages of quality assurance include: • Costs are reduced because there is less wastage and re-working of faulty products as the product is checked at every stage • It can help improve worker motivation as workers have more ownership and recognition for their work (see Herzberg) • It can help break down 'us and them' barriers between workers and managers as it eliminates the feeling of being checked up on • With all staff responsible for quality, this can help the firm gain marketing advantages arising from its consistent level of quality Total Quality Management (\"TQM\") This is a specific approach to quality assurance that aims to develop a quality culture throughout the firm. In TQM, organisations consist of 'quality chains' in which each person or team treats the receiver of their work as if they were an external customer and adopts a target of 'right first time' or zero defects. Quality Benchmarking Benchmarking is a general approach to business improvement based on best practice in the industry, or in another similar industry. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 73

Benchmarking enables a business to identify where it falls short of current best practice and determine what action is DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 74

needed to either match or exceed best practice. Done properly, benchmarking can provide a useful quality improvement target for a business. This can be a helpful approach for services as well as for products – for example a fast food business selling fish and chips could decide that it wanted to aim to equal McDonalds' speed of meeting customer orders for takeaway food. A financial services firm might want its call centre staff to answer 95% of telephone calls within six rings, if this is the practice of the best in the industry. In some cases, firms can use internal benchmarking in which best practice may be set with reference to another department, or by a similar factory in a different location. statistical quality control Statistical quality control (SQC) The application of statistical techniques to measure and evaluate the quality of a product, service, or process. Two basic categories: I. Statistical process control (SPC): - the application of statistical techniques to determine whether a process is functioning as desired II. Acceptance Sampling: - the application of statistical techniques to determine whether a population of items should be accepted or rejected based on inspection of a sample of those items. Quality Measurement: Attributes vs Variables Attributes: Characteristics that are measured as either \"acceptable\" or \"not acceptable\", thus have only discrete, binary, or integer values. Variables: Characteristics that are measured on a continuous scale. Page 75 Statistical Process Control (SPC) Methods Statistical process control (SPC) monitors specified quality characteristics of a product or service so as: DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

To detect whether the process has changed in a way that will affect product quality and To measure the current quality of products or services. Control is maintained through the use of control charts. The charts have upper and lower control limits and the process is in control if sample measurements are between the limits. Control Charts for Attributes P Charts - measures proportion defective. C Charts - measures the number of defects/unit. Control Charts for Variables X bar and R charts are used together - control a process by ensuring that the sample average and range remain within limits for both. Basic Procedure 1. An upper control limit (UCL) and a lower control limit (LCL) are set for the process. 2. A random sample of the product or service is taken, and the specified quality characteristicis measured. 3. If the average of the sample of the quality characteristic is higher than the upper control limit or lower than the lower control limit, the process is considered to be \"out of control\". CONTROL CHARTS FOR ATTRIBUTES p-Charts for Proportion Defective p-chart: a statistical control chart that plots movement in the sample proportion defective (p) over time Procedure: 1. take a random sample and inspect each item Page 76 DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

2. determine the sample proportion defective by dividing the number of defective items by the sample size DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 77

3. plot the sample proportion defective on the control chart and compare with UCL and LCL to determine if process is out of control The underlying statistical sampling distribution is the binomial distribution, but can be approximated by the normal distribution with: mean = u = np (Note - add the bars above the means used in all the equations in this section) standard deviation of p: sigmap = square root of (p(1 -p ) / n) where p = historical population proportion defective and n = sample size Control Limits: UCL = u + z sigmap LCL = u - z sigma p z is the number of standard deviations from the mean. It is set based how certain you wish to be that when a limit is exceeded it is due to a change in the process proportion defective rather than due to sample variability. For example: If z = 1 if p has not changed you will still exceed the limits in 32% of the samples (68% confident that mean has changed if the limits are exceeded. z = 2 - limits will be exceeded in 4.5 (95.5 % confidence that mean has changed) z = 3 - limits will be exceeded in .03 (99.7% confidence) c-Charts for Number of Defects Per Unit c-chart: a statistical control chart that plots movement in the number of defects per unit. Procedure: 1. randomly select one item and count the number of defects in that item 2. plot the number of defects on a control chart 3. compare with UCL and LCL to determine if process is out of control The underlying sampling distribution is the Poisson distribution, but can be approximated by the normal distribution DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 78

with: mean = c DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 79

standard deviation = square root of c where c is the historical average number of defects/unit Control Limits: UCL = c + z c LCL = c - z c Control Charts for Variables Two charts are used together: R-chart (\"range chart\") and X barchart (\"average chart\") Both the process variability (measured by the R-chart) and the process average (measured by the X bar chart) must be in control before the process can be said to be in control. Process variability must be in control before the X bar chart can be developed because a measure of process variability is required to determine the -chart control limits. R-Chart for Process Variability: UCLR = D4(R) LCLR = D3(R) where is the average of past R values, and D3 and D4 are constants based on the sample size -Chart for Process Average: UCLR = X bar + A2(R) LCL = X bar - A2(R) where X bar is the average of several past values, and A2 is a constant based on the sample size Other Types of Attribute-Sampling Plans Double-Sampling Plan: Specifies two sample sizes (n1 and n2) and two acceptance levels (c1 and c2) 1. if the first sample passes (actual defects c1), the lot is accepted 2. if the first sample fails and actual defects > c2, the lot is rejected 3. if first sample fails but c1 < actual defects c2, the second sample is taken and judged on the combined number of defectives found. Sequential-Sampling Plan: Each time an item is inspected, a decision is made whether to accept the lot, reject it, or continue sampling. Page 80 DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

Acceptance Sampling Goal: To accept or reject a batch of items. Frequently used to test incoming materials from suppliers or other parts of the organization prior to entry into the production process. Used to determine whether to accept or reject a batch of products. Measures number of defects in a sample. Based on the number of defects in the sample the batch is either accepted or rejected. An acceptance level c is specified. If the number of defects in the sample is c the atch is accepted, otherwise it is rejected and subjected to 100% inspection. Acceptance sampling involves both the producer (or supplier) of materials and the consumer (or buyer). Consumers need acceptance sampling to limit the risk of rejecting good-quality materials or accepting bad-quality materials. Consequently, the consumer, sometimes in con- junction with the producer through contractual agreements, specifies the parameters of the plan. Any company can be both a producer of goods purchased by another company and a consumer of goods or raw materials supplied by another company Sampling Plans All sampling plans are devised to provide a specified producer’s and consumer’s risk. However, it is in the consumer’s best interest to keep the average number of items inspected (ANI) to a minimum because that keeps the cost of inspection low. Sampling plans differ with respect to ANI. Three often-used attribute sampling plans are the single- sampling plan, the double-sampling plan, and the sequential-sampling plan. Analogous plans also have been devised for variable measures of quality. Single-Sampling Plan The single-sampling plan is a decision rule to accept or reject a lot based on the results of one random sample from the lot. The procedure is to take a random sample of size (n) and inspect each item. If the number of defects does not exceed a specified acceptance number (c), the consumer accepts the entire lot. Any defects found in the sample are either repaired or returned to the producer. If the number of defects in the sample is greater than c, the consumer subjects the entire lot to 100 percent inspection orrejects the entire lot and returns it to the producer. The single- sampling plan is easy to use but usually results in a larger ANI than the other plans. After briefly describing the other sampling plans, we focus our discussion on this plan Double-Sampling Plan In a double-sampling plan, management specifies two sample sizes( ) and two acceptance numbers ( ). If the quality of the lot is very good or verybad, the consumer can make a decision to accept or reject the lot on the basis of the first sample,which is smaller than in the single- sampling plan. To use the plan, the consumer takes a random sample of size . If the number of defects is less than or equal to , the consumer accepts thelot. If the number of defects is greater than , the consumer rejects the lot. If the number of defects is between , the consumer takes a second sample of size . If the combined number of defects in the two samples is less than or equal to , the consumer accepts the lot.Otherwise, it is rejected. A double-sampling plan can significantly reduce the costs of inspection relative to a single-sampling plan for lots with a very low or very high proportion defective because a decision can be made after DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 81

taking the first sample. However, if the decision requires two samples, the sampling costs can be greater than those for the single-sampling plan. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 82

Sequential-Sampling Plan A further refinement of the double-sampling plan is thesequential-sampling plan , in which the consumer randomly selects items from the lot and inspects them one by one. Each time an item is inspected, a decision is made to (1) reject the lot (2) accept the lot, or (3) continue sampling, based on the cumulative results so far. The analyst plots the total number of defectives against the cumulative sample size, and if the number ofdefectives is less than a certain acceptance number ( ), the consumer accepts the lot. If the number is greater than another acceptance number ( ), the consumer rejects the lot. If thenumber is somewhere between the two, another item is inspected. WORK STUDY Definition: Work study may be defined as the analysis of a job for the purpose of finding the preferred method of doing it and also determining the standard time to perform it by the preferred (or given) method. Work study, therefore, comprises of two areas of study: method study (motion study) and time study (work measurement). Role of Work Study in Improving Productivity In order to understand the role of work study, we need to understand the role of method study and that of time study. Method study (also sometimes called Work Method Design) is mostly used to improve the method of doing work. It is equally applicable to new jobs. When applied to existing jobs and existing jobs, method study aims to find better methods of doing the jobs that are economical and safe, require less human effort, and need shorter make-ready / put- away time. The better method involves the optimum use of best materials and appropriate manpower so that work is performed in well organized manner leading to increased resource utilization, better quality and lower costs. It can therefore be stated that through method study we have a systematic way of developing human resource effectiveness, providing high machine and equipment utilization, and making economical use of materials. Time study, on the other hand, provides the standard time, that is the time needed by worker to complete a job by the standard method. Standard times for different jobs are necessary for proper estimation of • manpower, machinery and equipment requirements • daily, weekly or monthly requirement of materials • production cost per unit as an input to better make or buy decision • labor budgets • worker's efficiency and make incentive wage payments. By the application of method study and time study in any organization, we can thus achieve greater output at less cost and of better quality, and hence achieve higher productivity. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 83

Work Study and Ergonomics The work study and the ergonomics are the two areas of study having the same objective: design the work system so that for the operator it is safe, and the work is less fatiguing and less time taking. METHOD STUDY Method study, aims to achieve the better method of doing work, and for this reason method study is sometimes called Work Method Design. Definition: Method study can be defined as the procedure for systematic recording, analysis and critical examination of existing or proposed method of doing work for the purpose of development and application of easier and more effective method. Method Study Procedure The following general steps describe the procedure for making a method study. 1. Select the job – on which method study is to be applied. 2. Obtain information and record. 3. Examine the information critically. 4. Develop the most practical, economical and effective method by considering real limitations of the situation. 5. Install the new method as standard practice. 6. Maintain the standard practice by regular follow up. Let us consider these steps in some detail. Selection of Job for Method Study Practically, any activity or a job is a potential project for improvement but as the work study engineer is to sell his ideas and maintain his existence in the organisation, he should always attempt to select those jobs for improvement which are unpopular among employees or are considered “dirty” by them. By improving such jobs, he would earn goodwill from the employees as well as the management, and can expect their full cooperation for other studies in the future. Considerations may be given to the following factors while selecting a job for method study Page 84 • Economic Factors DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

• Technical Factors • Human Factors Economic Factors: If the economic importance of a job is small, it is not wise to start or continue a long study. Priorities should be given to those types of job which offer greater potential for cost reduction. Such jobs are easily identifiable, as they have • High labour content, i.e. they consume more time • excessive machine or man idleness • higher frequency of occurrence, i.e. they have large demand • bottlenecks in production line • higher proportion of accidents • movement of material or men over long distance • high scrap and reprocessing costs • high payment of overtime bills. Technical Factors: The method study engineer must have the necessary technical knowledge about the job to be studied. Only surface knowledge about the subject may not lead to the right solution to the real problem. To illustrate, consider that a particular machine tool in proving bottleneck. The output from this machine is not reaching the assembly line in the required quantity. Through a preliminary study, it is found that it is running at lower speed and feed than that recommended for the pair of work and tool material used. Just increase in speed or feed may not be the solution of this problem. It may be possible that the machine itself is not rigid enough to operate at higher speeds or take a deeper cut. Just increase in speed may increase the output but the quality of job may be seriously affected. Technical expertise in machine tools and metal cutting process would be essential to solve problem of this kind. Human Factors: Emotional reaction of the workers to the method study and changes in method are important considerations. If the study of a particular job is suspected to cause unrest or ill feeling, it should not be undertaken, however useful it may be from the economic point of view. It is always better to take up first those jobs which are considered ‘dirty', unsafe, unpleasant, boring, or highly fatiguing, and improvements brought about as a result of method study. This would possibly ensure cooperative from the workers for the other jobs as well. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 85

After it is recognized that a problem exists, the first step is to properly formulate it. From the general statements like DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 86

“Costs are too high“, “Increase the production”, “Reduce shop floor accidents”, it is necessary to determine just what the real problem is. After it is ascertained that the problem merits consideration, it is decided whether this is the proper time to solve it, and how much time can be spent in solving it. The problem may then be defined broadly giving minimum constraints at this stage, as it will permit the use of imagination and creativity in finding a solution. It may sometimes be desirable to divide the complete problem into a couple of small problems and solve them. Information Collection And Recording Information Collection Techniques: The accuracy of data about the method study problem is important for the development of improved method. The following techniques are used for the collection of information / data about the task under consideration. These are not exclusive of each other, and for any particular method study problem, some or all the techniques may be employed. • Observation. It is a common technique used for collecting information about the present method or the existing problem. The method study person visits the site where the work is currently being done and observes various steps in the method being followed. There are many instances where all the data needed is obtained by only observing the work or work site. • Discussion. Discussion with those who do or who supervise the work can frequently provide information not obtainable by observation. The discussion technique is commonly used where irregular work is involved or where one is trying to analyze past work in order to improve efficiency of work to be done in future. Even where observation by itself may accomplish the data collection task, discussion may be used for developing good human relations. • Records. Valuable information can be obtained from past records concerning production, cost, time, inventory and sub-contracts. For certain type of information concerning the past practice, sometimes this is the only way to obtain authentic data. • Motion Pictures or video Films. Accurate and most detailed information can be obtained by taking motion pictures or video film. Information obtained by this procedure can easily be transmitted / forwarded to all levels in the organization and if needed, can be used directly for training purposes. The film can be used to focus attention at particular point or motion in an operation. For obtaining information concerning those types of work that involve large crew size, it is probably the only procedure. Information Recording Techniques: There are three main types of information recording techniques. These are Page 87 • Process Charts DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

• Diagrams DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 88

• Templates A Process Chart is a graphic means of representing the activities that occur during a manufacturing or servicing job. There are several types of process charts. These can be divided into two groups. (i) Those which are used to record a process sequence (i.e. series of events in the order in which they occur) but do not depict the events to time scale. Charts falling in this group are • Operation process chart • Flow process chart – (man / material / equipment type) • Operator chart (also called Two Handed Process Chart) (ii) Those which record events in the sequence in which they occur on a time scale so that the interaction of related events can be more easily studied. Charts falling in this group are • Multiple activity chart • Simo chart Diagrams. A diagram gives pictorial view of the layout of workplace or floor on which locations of different equipment, machines, etc. are indicated. The movement of subject (man or material) is then indicated on the diagram by a line or a string. The diagrams are valuable in highlighting the movement so that analyst can take steps to simplify or reduce it and thus effect saving in time or reduction in collisions / accidents. Two types of diagrams are common: Flow diagram and string diagram. Templates and 3-D models: Two-dimensional cut outs made from thin card sheet representing machinery, furniture, etc. can be used for developing new layouts and methods. The templates may have pieces of permanent magnet attached to them, so that when used on iron board; they remain glued on the board whenever placed. A scaled 3-D model of a working area helps easy understanding of lighting, ventilation, maintenance and safety DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 89

aspects that may be important in a method. Such models are often of great value in demonstrating the advantages of DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 90

the proposed changes to all concerned. However, their use is limited because of higher cost involved. Some computer softwares are available which help in constructing the layout and possibility of visualizing the working of process in a systematic way. Before taking up descriptions of these charts or diagrams, it is necessary to know the various elements of work. Elements of Work: There are five basic elements of work: Operation, Inspection, Transportation, Delay, and storage. Sometimes, more than one element occur simultaneously. It is shown as combined element with combined symbol. Examples are “Operation in combination will inspection”, and “Inspection in combination with Transportation”. Operation Process Chart: An operation process chart provides the chronological sequence of all operations and inspections that occur in a manufacturing or business process. It also shows materials used and the time taken by operator for different elements of work. Generally a process chart is made for full assembly, that is, it shows all the operations and inspections that occur from the arrival of raw material to the packaging of the finished product. Flow Process Chart: A flow process chart is used for recording greater detail than is possible in an operation process chart. It is made for each component of an assembly rather than for the whole assembly. A flow process chart shows a complete process in terms of all the elements of work. There are two main types of flow charts: product or material type , and the operator type . The product type records the details of the events that occur to a product or material, while the operator flow chart details how a person performs an operational sequence. An important and valuable feature of this chart is its recording of non-productive hidden costs, such as delays, temporary storages, unnecessary inspections, and unnecessary long distances traveled. When the time spent on these non productive activities is highlighted, analyst can take steps to minimize it and thus reduce costs. Operator Process Chart : It is also called Left Hand – Right Hand chart and shows the activities of hands of the operator while performing a task. It uses four elements of hand work: Operation, Delay (Wait), Move and Hold. Its main advantage lies in highlighting un-productive elements such as unnecessary delay and hold so that analyst can take measures to eliminate or shorten them. Multiple Activity Chart: DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 91

Worker-Machine process chart and gang process chart fall in the category of multiple activity charts. A worker- DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 92

machine chart is used for recording and analyzing the working relationship between operator and machine on which he works. It is drawn to time scale. Analysis of the chart can help in better utilization of both worker and machine time. The possibility of one worker attending more than one machine is also sought from the use of this chart. A gang process chart is similar to worker-machine chart, and is used when several workers operate one machine. The chart helps in exploring the possibility of reducing both the operator time and idle machine time. Simo Chart: A Simo chart is another Left-Hand Right-Hand chart with the difference that it is drawn to time scale and in terms of basic motions called therbligs. It is used when the work cycle is highly repetitive and of very short duration. Work Measurement Work measurement refers to the estimation of standard time for an activity, that is the time allowed for completing one piece of job by using the prescribed method. Standard time can be defined as the time taken by an average experienced worker for the job with provisions for delays beyond the worker's control. There are several techniques used for estimation of standard time in industry. These include time study, work sampling, standard data, and predetermined motion time system. Applications: Standard times for operations are useful for several applications in industry, like • Estimating material, machinery, and equipment requirements. • Estimating production cost per unit as an input to Preparation of budgets • Determination of selling price • Make or buy decision • Estimating manpower requirements. • Estimating delivery schedules and planning the work • Balancing the work of operators working in a group. • Estimating performance of workers and using that as the basis for incentive payment to those direct and indirector labor who show greater productivity. We will study some of the popular techniques of work measurement. TIME STUDY. It is the most versatile and the most widely used technique of work measurement. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 93

Definition: Time study is a technique to estimate the time to be allowed to a qualified and well-trained worker working at a normal pace to complete a specified task by using specified method. This technique is based on measuring the work content of the task when performed by the prescribed method, with the allowance for fatigue and for personal and unavoidable delays. Time Study Procedure: The procedure for time study can best be described step-wise, which are self explanatory. Step 1: Define objective of the study. This involves statement of the use of the result, the precision desired, and the required level of confidence in the estimated time standards. Step 2: Verify that the standard method and conditions exist for the operation and the operator is properly trained. If need is felt for method study or further training of operator, the same may be completed before starting the time study. Step 3: Select operator to be studied if there are more than one operator doing the same task. Step 4: Record information about the standard method, operation, operator, product, equipment, and conditions on the Time Study observation sheet. Step 5: Divide the operation into reasonably small elements, and record them on the Time Study observation sheet. Step 6: Time the operator for each of the elements. Record the data for a few number of cycles on the Time Study observation sheet. Use the data to estimate the total number of observations to be taken. Step 7: Collect and record the data of required number of cycles by timing and rating the operator. Step 8: Calculate the representative watch time for each element of operation. Multiply it by the rating factor to get normal time. Normal time = Observed time x Rating factor Calculate the normal time for the whole operation by adding the normal time of its various elements. Step 9: Determine allowances for fatigue and various delays. Step 10: Determine standard time of operation. Standard time = Page 94 DR NAVEEN PRASADULA MSC (I.T), MBA, PHD

Normal time + allowances Selection of job for Time Study DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 95

Time Study is conducted on a job • which has not been previously time-studied. • for which method change has taken place recently. • for which worker(s) might have complained as having tight time standards. Selection of Worker for Time Study The selection of worker for time study is a very important factor in the success of the study. If there is only one person on the job, as usually is, then there is no choice. But if more than one person is performing the same operation, the time study man may time one or more of the workers. If all the workers are using the same method for doing the job and there is different in the rate of their doing it, it is necessary to select a suitable worker for the study. The worker on which time study should be conducted must • have necessary skill for the job. • have sufficient experience with the given method on the job (that is, he should have crossed the learning stage). • be an ‘average' worker as regards the speed of working. • be temperamentally suited to the study (those who can't work in normal fashion when watched, are not suitable for the study). • have knowledge about the purpose of study. Time Study Equipment The following equipment is needed for time study work. • Timing device • Time study observation sheet • Time study observation board • Other equipment Timing Device. The stop watch is the most widely used timing device used for time study, although electronic timer is also sometimes used. The two perform the same function with the difference that electronic timer can measure time to the second or third decimal of a second and can keep a large volume of time data in memory. DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 96

Time Study Observation Sheet. It is a printed form with spaces provided for noting down the necessary information about the operation being studied, like name of operation, drawing number, and name of the worker, name of time study person, and the date and place of study. Spaces are provided in the form for writing detailed description of the process (element-wise), recorded time or stop-watch readings for each element of the process, performance rating(s) of operator, and computation shows a typical time study observation sheet. Time Study Board. It is a light -weight board used for holding the observation sheet and stopwatch in position. It is of size slightly larger than that of observation sheet used. The board has a clamp to hold the observation sheet. During the time study, the board is held against the body and the upper left arm by the time study person in such a way that the watch could be operated by the thumb/index finger of the left hand. Watch readings are recorded on the observation sheet by the right hand. Other Equipment. This includes pencil, eraser, device like tachometer for checking the speed, etc. Dividing Work into Short Elements Timing a complete task as one element is generally not satisfactory. For the purpose of time study the task is normally broken into short elements and each element is timed separately, for the following reasons: (1) To separate unproductive part of task from the productive one. (2) To improve accuracy in rating. The worker may not work at the same speed throughout the cycle. He may perform some elements faster and some slower. Breaking of task into short elements permits rating of each element separately which is more realistic than just rating once for the complete cycle. (3) To identify elements causing high fatigue. Breaking of task into short elementspermits giving appropriate rest allowances to different elements. (4) To have detailed job specifications. This helps in detection of any variation in the method that may occur after the time standard is established. (5) To prepare standard data for repeatedly occurring elements. The following guidelines should be kept in mind while dividing a task into elements. • The elements should be of as short duration as can be accurately timed. (This in turn, depends on the skill of the time study man, method of timing and recording, and many other factors. Generally, with the stop watch, elements of duration less than 0.03 to 0.05 minute are difficult to time accurately. The elements should not normally be longer than 0.40 min.). DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 97

• Manually performed elements should be separated from machine paced elements. (Time for machine paced elements DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 98

can be determined by calculation). Machine elements are not rated against a normal. This rule also helps in recognition of delays. • Constant elements should be separated from variable elements. (Constant elements are those elements which are independent of the size, weight, length, or shape of the workpiece. or example, the time to pick screw driver from its place and bring it to the head of a screw is constant, whereas the time to tighten or loosen the screw is a variable, depending upon the length and size of the screw). • The beginnings and endings of elements should be easily distinguishable. These should preferably be associated with some kind of sound. • Irregular elements, those not repeated in every cycle, should be separated from regular elements. For example, if the jig is cleaned off after every ten parts produced, \"cleaning\" is an irregular element, and its time should be spread over ten cycles. • Unnecessary motions and activities should be separated from those considered essential. • Foreign or accidental elements should be listed separately. Such elements are generally of non-repetitive type. Number of cycles to be timed. The following general principles govern the number of cycles to get the representative average cycle time. • Greater the accuracy desired in the results, larger should be the number of cycles observed. • The study should be continued through sufficient number of cycles so that occasional elements such as setting-up machine, cleaning of machine or sharpening of tool are observedfor a good number of times. • Where more than one operator is doing the same job, short study (say 10 to 15 cycles) should be conducted on each of the several operators than one long study on a single operator. It is important that enough cycles are timed so that reliable average is obtained. Following techniques are used to determine the number of cycles to be timed. (i) Use of Tables: On the consideration of the cost of obtaining the data and the desired accuracy in results, most companies have prepared their own tables for the use of time study people, which indicate the number of cycles to be timed as a function of the cycle time and the frequency of occurrence of the job in the company. (ii) (ii) Statistical methods: On the basis of the requirements of the particular situation involved, accuracy and confidence level are decided (An accuracy of a confidence level of 95% is considered reasonable in most cases). A preliminary study is conducted in which some (say N) cycles are timed. Standard deviation o of these (N) observations is calculated as WORK SAMPLING Work Sampling (also sometimes called ratio delay study) is a technique of getting facts about utilization of machines or human beings through a large number of instantaneous observations taken at random time intervals. The ratio of observations of a given activity to the total observations approximates the percentage of time that the process is in that DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 99

state of activity. For example, if 500 instantaneous observations taken at random intervals over a few weeks show that a lathe operator was doing productive work in 365 observations and in the remaining 135 observations he was found DR NAVEEN PRASADULA MSC (I.T), MBA, PHD Page 100